JP2002199604A - Charging control circuit and electronic device having charging control function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fixed loss consumed in a charging circuit and prevent heating in the charging circuit even when a DC power supply source having a substandard large charging capacity is connected to the charging circuit. SOLUTION: The charging control circuit, which is connected to a DC power source 14 having a prescribed charging capacity and supplies a secondary battery 15 a constant current and/or a constant voltage according to the DC power source 14, has a charging circuit 11 which is serially connected between the DC power source 14 and the secondary battery 15 and adjusts the charging current from the DC power source 14 to the secondary battery 15, a voltage detection circuit 12 which detects a serial voltage drop according to the voltage of both ends of the charging circuit 11, and at least a control circuit 13 which makes the internal resistance of the charging circuit 11 variable according to at least the serial voltage drop detected by the voltage detection circuit 12. If the DC power source 14 having a large charging capacity of out of standard is connected to this charging control circuit 100, the internal resistance of the charging circuit 11 is increased by the control circuit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge control circuit and an electronic device having a charge control function suitable for a battery-operated portable telephone, a portable terminal device, a video camera and the like.

[0002]

2. Description of the Related Art In recent years, rechargeable batteries (secondary batteries) have been widely used as power sources in portable telephones and portable terminal devices. This is due to the development of secondary batteries with a large charge capacity and the fact that secondary batteries are more environmentally friendly than non-rechargeable primary batteries.

FIG. 11A is an image diagram showing an example of charging using an AC adapter. Mobile phone 1 shown in FIG. 11A
A plug-in type AC adapter 1 is connected to 01, and a secondary battery built in the mobile phone is charged. AC adapter 1
Is usually sold as a set with an electronic device. A DC plug 3 is connected to the end of the power cord extending from the AC adapter 1, and the DC plug 3 is connected to the mobile phone 101. The charging capacity is determined by the total charging time T [h] and the charging current I
The product of [A], that is, Ah.

FIG. 11B is an image diagram showing a charging example using the stationary charger 2. The mobile phone 101 shown in FIG. 11B is set upright on the stationary charger 2, and the secondary battery built in the mobile phone is charged for a predetermined time. The stationary charger 2 is also a mobile phone 10
Sold as a set with one. Although it depends on the electronic device such as the mobile phone 101, the AC adapter 1 has a charging voltage of 5V and a charging current of approximately 0.6A when the driving voltage of the electronic device is approximately 4.2V, for example. The drive voltage of the electronic device is 6.0
In the case of about V, the charging voltage is 8 V and the charging current is 0.8 A
It is about. When the driving voltage of the electronic device is about 7.5 V, the charging voltage is 10 V and the charging current is about 1.0 A.

[0005] By the way, according to the charging example according to the conventional method, the AC adapter 1 sold as a set with an electronic device,
When the stationary charger 2 or the like is normally used, the charging voltage and the charging current required by the electronic device are maintained, so that no trouble occurs.

[0006]

However, when a plurality of AC adapters 1 having different charging characteristics, stationary chargers 2 and the like are mixed, an AC adapter having a predetermined charging capacity is required.
It is assumed that a DC power supply having a large non-standard charging capability is erroneously connected to the electronic device dedicated to the adapter.

[0007] When a DC power supply having such a large non-standard charging capability is connected to the electronic equipment, the fixed loss consumed by the charging control circuit increases, and the charging circuit generates heat, which in turn causes the electronic device to generate heat. There is a problem that the equipment is heated.

Therefore, the present invention solves such a conventional problem. Even when a DC power supply having a large non-standard charging capability is connected to the charging circuit, the DC power is consumed by the charging circuit. It is an object of the present invention to provide a charge control circuit and an electronic device with a charge control function which can suppress fixed loss and prevent the charging circuit from being heated.

[0009]

SUMMARY OF THE INVENTION The above-mentioned problem is solved by connecting to a DC power supply having a predetermined charging ability and supplying a constant current and / or a constant voltage to a secondary battery based on the DC power supply. In the controlling circuit, a charging circuit that is connected in series between the DC power supply and the secondary battery and adjusts a charging current from the DC power supply to the secondary battery, based on a voltage across the charging circuit. A charge control circuit comprising: a voltage detection circuit for detecting a series voltage drop; and a control circuit for varying an internal resistance of the charging circuit based on at least the series voltage drop detected by the voltage detection circuit. Solved by

According to the charge control circuit of the present invention, when charging is controlled to supply a constant current and a constant voltage to a secondary battery based on a DC power supply having a predetermined charging capability, the DC power supply The charging current from the DC power supply to the secondary battery is adjusted by a charging circuit connected in series with the secondary battery. The series voltage drop of this charging circuit is detected by the voltage detection circuit. The control circuit varies the internal resistance of the charging circuit based on the series voltage drop detected by the voltage detection circuit.

For example, when a DC power supply having a large non-standard charging capability is connected to the charging control circuit, and the DC power supply having a predetermined charging capability is connected, the DC power supply is compared with the series voltage drop of the charging circuit. When the series voltage drop increases, the internal resistance of the charging circuit is increased by the control circuit.

Therefore, when a DC power supply having a large non-standard charging capacity is connected to the charging control circuit, compared with a case where the DC power supply is connected to the DC power supply having a predetermined charging capacity.
The charging current can be kept low. As a result, even when a non-standard DC power supply is connected, the fixed loss consumed in the charging circuit can be suppressed low, and heat generation in the charging circuit can be suppressed.

An electronic device with a charge control function according to the present invention is an electronic device that operates using a secondary battery as a driving power source, is connected to a DC power source having a predetermined charging capability, and is configured to operate based on the DC power source. A charge control circuit that supplies a constant current and / or a constant voltage to the secondary battery; the charge control circuit is connected in series between the DC power supply and the secondary battery, and is connected to the secondary battery from the DC power supply. A charging circuit for adjusting a charging current of the charging circuit; a voltage detecting circuit for detecting a series voltage drop based on a voltage between both ends of the charging circuit; and a charging circuit based on at least the series voltage drop detected by the voltage detecting circuit. And a control circuit for varying the internal resistance.

According to the electronic device having the charge control function of the present invention, the above-described charge control circuit is applied, so that even when a nonstandard DC power supply is connected, the fixed loss consumed by the charge circuit is reduced. It can be kept low.

Therefore, not only when the battery is connected to a DC power source having a predetermined charging capability but also when a nonstandard DC power source is connected, it is possible to protect an electronic device that operates using the secondary battery as a drive power source. .

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a charge control circuit and an electronic device with a charge control function according to the present invention will be described with reference to the drawings.

(1) Embodiment FIG. 1 shows a charge control circuit 10 as an embodiment according to the present invention.
FIG. 4 is a block diagram showing an example of the configuration of 0. In this embodiment, a charge control circuit is provided for controlling a charge current from a DC power supply to a secondary battery, and an internal resistance of the charge circuit is adjusted based on a series voltage drop of the charge circuit for adjusting the charge current by the charge control circuit. By changing the minute, even when a DC power supply having a large non-standard charging capability is connected to the charging control circuit, it is possible to suppress the fixed loss consumed in the charging circuit and to heat the charging circuit. Is to be prevented.

A charging control circuit 100 shown in FIG. 1 is connected to a DC power supply 14 having a predetermined charging capacity, and based on the DC power supply 14, supplies a constant current and / or a constant voltage to the secondary battery 1.
5 is a circuit for controlling charging so as to be supplied to the power supply 5. As the DC power supply 14, a plug-in type AC adapter, a stationary charger, or the like is used. This charge control circuit 100
It has three terminals a, b, c, d. A DC power supply 14 is connected to the input terminal ab, and a secondary battery 15 is connected to the output terminal cd. As the secondary battery 15, a Ni-Cd battery or a lithium battery is used. The input terminal b and the output terminal d are connected by a ground line GND and are grounded.

The input terminal a to which the DC power source 14 is connected
A charging circuit 11 is connected in series between the DC power supply 14 and the output terminal c to which the secondary battery 15 is connected.
To adjust the charging current to the secondary battery 15. The charging circuit 11 includes a transistor for adjusting the charging current I, a constant current element for protecting the transistor, and the like. As the transistor, a pnp bipolar transistor or a power MOS transistor is used. A resistor is used for the constant current element.

A voltage detecting circuit 12 is connected in parallel to an input point (terminal a) and an output point (terminal c) of the charging circuit 11, and detects a series voltage drop based on the voltage across the charging circuit 11. It is made to do. Here, assuming that the series voltage drop is Vac, the voltage between the input terminals ab, that is, the output voltage of the DC power supply 14 is VIN, and the voltage between the output terminals cd, that is, the output voltage of the secondary battery 15 is VOUT, Vac = VIN−VOUT.

A control circuit 13 is connected between the voltage detection circuit 12 and the charging circuit 11, and based on at least the internal resistance Rac of the charging circuit 11 based on the series voltage drop Vac detected by the voltage detection circuit 12. Is made to be variable. This is for protecting the charging circuit 11.

FIG. 2 is a diagram showing an example of an equivalent circuit of the charge control circuit 100. The charging circuit 11 shown in FIG. 2 is generally represented by a variable resistor connected between the input and output terminals ac, and is replaced with, for example, a current divider having a movable piece n connected to the output terminal c side. The secondary battery 15 is also represented by a variable resistor. This is because a difference occurs between the terminal voltage Vup at the time of full charge and the terminal voltage Vdw at the time of discharge.

Here, the case where the movable piece n shown in FIG. 2 is located near the input terminal a indicates a state where the resistance value is the smallest. Here, assuming that the series resistance (minute) of the charging circuit 11 is Rac and the charging current flowing through the series resistance Rac is I, the series voltage drop Vac is V1 = I · Rac.
Assuming that the series resistance Rac in this state is r1, I ² · r1
Fixed loss P0 occurs.

Conversely, the case where the movable piece n is located near the output terminal c indicates the state where the resistance value is the largest. The series voltage drop Vac is V2, and the series resistance Rac is r2
It is. There is a relationship of V2> V1 and r2> r1 between them. Depending on the circuit design, V2 and V1, r2 and r1
The difference between them is several tens of times.

Next, an operation example of the charge control circuit 100 will be described. For example, a DC power supply 14 having a predetermined charging capability is connected to the input terminal ab shown in FIG. 2, and a constant current and a constant voltage are supplied to the secondary battery 15 based on the DC power supply 14.
When charging control to supply power to
Charging circuit 1 connected in series between battery 4 and secondary battery 15
1, the charging current I from the DC power supply 14 to the secondary battery 15 is adjusted and supplied.

The series voltage drop Vac of the charging circuit 11
Is detected by the voltage detection circuit 12. Control circuit 13
In FIG. 2, the movable piece n shown in FIG. 2 has the minimum internal resistance Rac based on the series voltage drop Vac detected by the voltage detection circuit 12.
It is adjusted to move to (closer). If the series resistance Rac in this case is r1, a fixed loss P0 of I ² · r1 occurs.

When the input terminal ab shown in FIG. 2 is connected to the charging control circuit 100 with a DC power supply 14 having a large nonstandard charging capability, the control circuit 13 supplies a DC power having a predetermined charging capability. The resistance of the charging circuit 11 is increased as compared with the case where the power supply 14 is connected. For example, the internal resistance Rac of the charging circuit 11 becomes the largest,
The movable piece n shown in FIG. 2 is adjusted to the position where it moves (toward the output terminal c).

[0028] When the series resistance Rac in this case and r2, occurs I 'fixed loss of ² · r2 P0'. By making the fixed loss P0 equal to the fixed loss P0 ', heating can be prevented even when the DC power supply 14 having a large non-standard charging capability is connected to the charging control circuit 100. Specifically, to vary the internal resistance Rac of the charging circuit 11, the internal resistance of the charging control transistor is set to r1
This is made possible by controlling from r to r2.

As described above, the charge control circuit 1 according to the present invention
According to 00, a DC power supply 14 having a large non-standard charging capability is connected to the charge control circuit 100, and a series voltage drop Vac = V1 when the DC power supply 14 having a predetermined charging capability is connected. , The series voltage drop V
2 increases, the internal resistance R of the charging circuit 11 increases.
ac is increased from r1 to r2 by the control circuit 13.

Therefore, when the DC power supply 14 having a large non-standard charging capability is connected to the charging control circuit 100, the charging current is higher than when the DC power supply 14 is connected to the DC power supply 14 having the predetermined charging capability. I can be suppressed to a low charging current I ′ of about several tenths. Accordingly, even when the non-standard DC power supply 14 is connected, the fixed loss P0 ′ consumed in the charging circuit 11 can be suppressed low, and heat generation in the charging circuit 11 can be suppressed.

(2) First Embodiment FIG. 3 is a circuit diagram showing a configuration example of a charge control circuit 201 as a first embodiment according to the present invention. In this example,
A charging control circuit 20 for supplying a charging current from an AC adapter as an example of a DC power supply to a secondary battery such as a Ni-Cd battery.
1. The internal resistance of the charge control transistor of the constant voltage / constant current circuit is varied based on the series voltage drop of the constant voltage / constant current circuit for adjusting the charging current by the charge control circuit 201, Even when an external AC adapter having a large charging capability is connected to the charging control circuit 201, the fixed loss consumed in the constant voltage / constant current circuit can be suppressed and the heating of the constant voltage / constant current circuit can be suppressed. It is something that can be prevented.

The charging control circuit 201 shown in FIG. 3 is connected to the AC adapter 1 having a predetermined charging capability.
This is a circuit that controls charging to supply a constant current and / or a constant voltage to the secondary battery 15 based on the adapter 1. AC
As the adapter 1, a plug-in type AC adapter is used. The charge control circuit 201 has four terminals a, b, c,
d.

The input terminal ab is connected to the AC adapter 1, and the output terminal cd is connected to the secondary battery 15 through the charge switch SX. Charge switch SX is AC
When the plug of the adapter is inserted into the input terminal ab, the adapter is disconnected from the load circuit and is automatically connected to the charge control circuit 201. As the secondary battery 15, a Ni-Cd battery is used. Ground line G between input terminal b and output terminal d
Connected at ND and grounded.

Between the input terminal a to which the AC adapter 1 is connected and the output terminal c to which the secondary battery 15 is connected,
A constant voltage / constant current circuit 21 as an example of a charging circuit is connected in series, and adjusts a charging current from the AC adapter 1 to the secondary battery 15.

The constant voltage / constant current circuit 21 has a resistor R1, a charge control transistor Q1, a constant voltage diode DZ1, and a resistor R7. One end of a resistor R1, which is an example of a constant current element, is connected to the input terminal a, and the other end is connected to the emitter of the transistor Q1, so as to protect the transistor Q1 from overcurrent. Transistor Q1
Is connected to the output terminal c.

A pnp bipolar transistor is used as the transistor Q1. The output terminal c is connected to the cathode of the constant voltage diode DZ1, and the anode of the diode DZ1 is connected to one end of the resistor R7 so that the output terminal cd is kept constant. Resistance R7
Is connected to a ground line GND. Here, the connection point between the diode DZ1 and the resistor R7 is defined as p1.

An output fluctuation detecting circuit 12 is connected in parallel to an input point (terminal a) and an output point (terminal c) of the constant voltage / constant current circuit 21. Based on this, the series voltage drop Vac is detected. The series voltage drop Vac is given by: Vac = VIN−VOU
Given by T. The output fluctuation detecting circuit 12 includes a transistor Q2 for controlling internal resistance, a resistor R2, and an error amplifying circuit 8.
A, and resistors R5 and R6.

The input terminal a is connected to the emitter of the transistor Q2, and a base bias resistor R2 is connected between the base of Q2 and the emitter of Q1. A pnp bipolar transistor is also used as the transistor Q2. A resistance dividing circuit in which resistors R5 and R6 are connected in series is connected between the output terminals cd to detect an output voltage. The connection point p2 between the resistors R5 and R6 is connected to the minus terminal of the error amplification circuit 8A, and the connection point p1 between the diode DZ1 and the resistance R7 is connected to the plus terminal of the error amplification circuit 8A.

Further, a control circuit 13 is connected between the base of the transistor Q1 and the ground line GND, and based on at least the series voltage drop Vac detected by the output fluctuation detection circuit 12, the constant voltage / constant current circuit 21 is provided. Resistance of the charge control transistor Q1 (internal resistance Ra
c) is made variable. Constant voltage constant current circuit 21
In order to protect.

The control circuit 13 has resistors R3 and R4 and a transistor Q3 for controlling a base current. One end of the resistor R3 is connected to the base of the transistor Q1, and the other end of the resistor R3 is connected to the collector of the transistor Q3. An npn-type bipolar transistor is used as the transistor Q3. The output of the error amplifier circuit 8A is connected to the base of the transistor Q3.
The emitter of No. 3 is grounded through a resistor R4.

Next, an operation example of the charge control circuit 201 will be described. For example, an AC adapter 1 having a predetermined charging capability is connected to the input terminal ab shown in FIG. 3, and a constant current and a constant voltage are supplied to the secondary battery 1 based on the AC adapter 1.
5 for charging control, the AC adapter 1
A constant-voltage / constant-current circuit 21 connected in series between the AC adapter 1 and the secondary battery 15
Is adjusted and supplied.

The serial voltage drop Vac of the constant voltage / constant current circuit 21 is detected by differentially amplifying the output voltage VOUT divided by the resistors R5 and R6, the diode DZ1 and the resistor R7 by the error amplifier circuit 8A. You. The error voltage Vε by the error amplification circuit 8A is
3 is input to the base of the transistor Q3. The transistor Q3 is turned on or off based on the error voltage Vε depending on the series voltage drop Vac detected by the error amplifier circuit 8A.

When the error voltage Vε is small, that is, when Vac = V1 described with reference to FIG. 2, the transistor Q3 remains off. Therefore, transistor Q
2 increases, the collector potential VCE of the transistor Q2 decreases, and the base potential VBE of the transistor Q1 increases, turning on the transistor Q1. This is equivalent to the state in which the movable piece n shown in FIG. 2 is moved (closer to the input terminal a) as shown in FIG. 2 in which the internal resistance (the internal resistance Rac) of the transistor Q1 of the constant voltage / constant current circuit 21 is minimized. In this case, the internal resistance of the transistor Q1 is represented by r
If it is set to 1, a fixed loss P0 of I ² · r1 occurs.

When an AC adapter 1 'having a large non-standard charging capability is connected to the input control terminal 201 of the input terminal ab shown in FIG.
Compared to the case where the adapter 1 is connected, the transistor Q1
Is controlled such that the internal resistance of the second line is set to r2. That is,
The error voltage Vε by the error amplification circuit 8A is input to the base of the transistor Q3 of the control circuit 13, but Vε is
The output value is several tens times higher than that of the adapter 1. Therefore,
The transistor Q3 is turned on based on the error voltage Vε depending on the series voltage drop Vac detected by the error amplifier circuit 8A.

As a result, the base potential V BE of the transistor Q2 decreases, and the collector potential V
CE rises, the base potential VBE of transistor Q1 falls, and transistor Q1 turns off. This is equivalent to a state in which the movable piece n shown in FIG. 2 has moved (closer to the output terminal c) as shown in FIG. 2 in which the internal resistance (the internal resistance Rac) of the transistor Q1 of the constant voltage / constant current circuit 21 is the largest.

If the series resistance Rac is r2 in this case, a fixed loss P0 ′ of I ′ ² · r2 occurs, but the charging current I ′ becomes several tens of times smaller than when the AC adapter 1 is connected. The fixed loss P0 and the fixed loss P
0 ′ can be made substantially equal. Therefore, even when the AC adapter 1 ′ having a large non-standard charging capability is connected to the charging control circuit 201, it is possible to suppress heat generation in the constant voltage / constant current circuit 21.

FIG. 4 is a diagram showing an example of charging characteristics when an AC adapter having a predetermined charging capability is connected. In this example, an AC adapter 1 of an output voltage VIN = 5 V and a charging current I = 0.6 A (an adapter and an electronic device are sold as a pair) is used.
Is used. The vertical axis represents the voltage V and the current I.

In this example, the terminal voltage (reference value) Vup at the time of full charge of the secondary battery is 4.2 V, and the terminal voltage V at the time of discharge is
When dw is 3.0 V, the output voltage VOUT is 4.2
V, and the charging current I is made 0.6 A. Therefore, the series voltage drop Vac is 0.8 V, and the fixed loss P0 in the constant voltage constant current circuit 21 is 0.48 W.

The terminal voltage Vdw = 3.0 V of the secondary battery recovers to the terminal voltage Vup = 4.2 V as charging proceeds. The charge time from the charge start time t0 to the full charge is tx
Then, the charging time is represented by Tf = tx-t0. The charge capacity is Tf · I [Ah]. After the full charge, the charging current I decreases exponentially, and the terminal voltage Vup of the secondary battery becomes substantially equal to the output voltage VIN of the AC adapter 1 = 5V.

FIG. 5 is a diagram showing an example of charging characteristics when an AC adapter having a nonstandard charging capability is connected. In this example, the output voltage VIN = 8V, the charging current I = 1.0A,
This is the case where the C adapter 1 'is used. The vertical axis represents the voltage V and the current I.

Also in this example, the terminal voltage Vup when the secondary battery is fully charged is set to 4.2 V, and the terminal voltage Vdw when discharging is set to 3.
When the voltage is 0 V, the output voltage VOUT is 8.0 V,
The series voltage drop Vac is 3.8V. However, the internal resistance of the charge control transistor Q1 becomes about 30 times that of the standard AC adapter, and the charge current I ′ is suppressed to about 0.1 A. The fixed loss P0 'can be suppressed to about 0.38W.

The control circuit 13 sets the internal resistance of the transistor Q1 to r1 =
Control is performed such that r2 = about 38Ω from about 1.33Ω. Therefore, A having a large non-standard charging capacity
Even when the C adapter 1 'is connected to the charge control circuit 201, heat generation in the constant voltage / current circuit 21 can be suppressed.

The terminal voltage Vdw = 3.0 V of the secondary battery recovers to the terminal voltage Vu = 4.2 V as charging proceeds.
Assuming that a charging time from the charging start time t0 to a full charge is tx ′, the charging time is represented by Tf ′ = tx′−t0.
The charge capacity is Tf ′ · I ′ [Ah]. Since the charging current I 'is suppressed to approximately 1/6 times the charging current I when the standard AC adapter is connected, the charging time is required to be six times or more as long as the standard time.

(3) Second Embodiment FIG. 6 is a circuit diagram showing a configuration example of a charge control circuit 202 as a second embodiment according to the present invention. In this embodiment, a charge control circuit 202 is provided. The charge control circuit 202 controls the internal resistance of the charge control transistor Q1 through the internal resistance control transistors Q2 and Q4, thereby providing a large non-standard charge capability. Even when the AC adapter is connected to the charging control circuit 202, the fixed loss consumed in the constant voltage / constant current circuit 21 can be suppressed and the constant voltage / constant current circuit 21 can be prevented from being heated. Things.

The charge control circuit 202 shown in FIG. 6 includes an input / output voltage detection circuit 16, a control circuit 17, and a constant voltage / constant current circuit 2.
One. The components having the same names and the same reference numerals as those in the first embodiment have the same functions, and the description thereof will be omitted.

An input / output voltage detection circuit 16 is connected in parallel to an input point (terminal a) and an output point (terminal c) of the constant voltage / constant current circuit 21. Based on this, the series voltage drop Vac is detected. The input / output voltage detection circuit 16 includes resistors R8, R9, R
13, R14 and an error amplifier circuit 8B.

A resistor dividing circuit in which resistors R8 and R9 are connected in series is connected between the input terminals ab to detect the input voltage VIN. A connection point p1 between the resistors R8 and R9 is connected to a negative terminal of the error amplifier circuit 8B. A resistance dividing circuit in which resistors R13 and R14 are connected in series is connected between the output terminals cd to detect the output voltage VOUT. The connection point p2 between the resistors R13 and R14 is connected to the + terminal of the error amplifier circuit 8B.

The control circuit 17 includes resistors R2, R11, R1
2. It has transistors Q2 and Q4 for controlling the internal resistance. The input terminal a is connected to the emitter of the transistor Q2, and a base bias resistor R2 is connected between the base of Q2 and the emitter of Q1. The collector of Q2 is connected to the base of Q1. Transistor Q
2 is a pnp bipolar transistor.

The base of the transistor Q2 is connected to the collector of the transistor Q4 via the resistor R11, and the base of the transistor Q4 is connected to the output of the error amplifier 8B. The emitter of transistor Q4 is grounded through resistor R12. An npn-type bipolar transistor is used as the transistor Q4.

Next, an operation example of the charge control circuit 202 will be described. For example, when an AC adapter having a large non-standard charging capability is connected to the input terminal ab shown in FIG. 6, the control circuit 17 reduces the internal resistance of the transistor Q1 as compared with the case where a standard AC adapter is connected. Control is performed to set r2. That is, the input voltage VIN divided by the resistors R8 and R9 is detected in the error amplifier circuit 8B, the output voltage VOUT divided by the resistors R13 and R14 is detected, and the input voltage VIN and the output voltage VOUT are amplified by the error amplifier. The signal is differentially amplified by the circuit 8B.

The error voltage Vε generated by the error amplifier circuit 8B
Is input to the base of the transistor Q4 of the control circuit 17, and Vε has an output value several tens of times higher than the standard value.
Therefore, in the transistor Q4, the error voltage V that depends on the series voltage drop Vac detected by the error amplifier circuit 8B.
Turns on based on ε.

As a result, the base potential V BE of the transistor Q2 decreases, and the collector potential V
CE rises, the base potential VBE of transistor Q1 falls, and transistor Q1 turns off. This is equivalent to a state in which the movable piece n shown in FIG. 2 has moved (closer to the output terminal c) as shown in FIG. 2 in which the internal resistance (the internal resistance Rac) of the transistor Q1 of the constant voltage / constant current circuit 21 is the largest.

If the series resistance Rac is r2 in this case, a fixed loss P0 ′ of I ′ ² · r2 occurs. However, since the charging current I ′ is reduced to about several tenths of the standard value, The loss P0 and the fixed loss P0 ′ can be made substantially equal. Therefore, even when an AC adapter having a large non-standard charging capability is connected to the charging control circuit 202, heat generation in the constant voltage / constant current circuit 21 can be suppressed. The description of the operation when the AC adapter having the standard charging capability is connected is omitted.

(4) Third Embodiment FIG. 7 is a circuit diagram showing a configuration example of a charge control circuit 203 as a third embodiment according to the present invention. In this embodiment, a charge control circuit 203 is provided. In this charge control circuit 203, the function of the output fluctuation detection circuit according to the first embodiment and the function of the input / output voltage detection circuit according to the second embodiment are combined. By controlling the internal resistance of the charge control transistor Q1 through the resistance control transistors Q2 to Q4, even if an AC adapter having a large non-standard charge capability is connected to the charge control circuit 203, the constant voltage is maintained. The configuration is such that the fixed loss consumed in the constant current circuit 21 can be suppressed and the constant voltage constant current circuit 21 can be prevented from being heated.

The charge control circuit 203 shown in FIG. 7 includes an input / output voltage detection circuit 18, a control circuit 19, and an output fluctuation detection circuit 20.
And a constant-voltage / constant-current circuit 21. The components having the same names and the same reference numerals as those in the first and second embodiments have the same functions, and thus the description thereof will be omitted.

A voltage detection circuit 20 is connected to the output terminal c of the constant voltage / current circuit 21. The voltage detection circuit 20 includes an error amplification circuit 8A, resistors R5 to R7, and a diode DZ1.
have. This output terminal c has a constant voltage diode D
The cathode of Z1 is connected, the anode of this diode DZ1 is connected to one end of the resistor R7, and the output terminal cd is kept constant. The other end of the resistor R7 is connected to the ground line GND. Here, the diode DZ1 and the resistor R
The connection point with 7 is p11.

A resistance dividing circuit in which resistors R5 and R6 are connected in series is connected between the output terminals cd to detect an output voltage. The connection point p12 of the resistors R5 and R6 is connected to the minus terminal of the error amplification circuit 8A,
A terminal is a connection point p11 between the diode DZ1 and the resistor R7.
Is connected.

The input / output voltage detecting circuit 18 is connected in parallel to the constant voltage / constant current circuit 21 so as to detect a series voltage drop Vac based on the voltage between both ends of the constant voltage / constant current circuit 21. You. The input / output voltage detection circuit 18 has resistors R8, R9, R13, R14 and an error amplification circuit 8B.

A resistor dividing circuit in which resistors R8 and R9 are connected in series is connected between the input terminals ab to detect the input voltage VIN. A connection point p21 between the resistors R8 and R9 is connected to a negative terminal of the error amplifier circuit 8B. A resistance dividing circuit in which resistors R13 and R14 are connected in series is connected between the output terminals cd to detect the output voltage VOUT. A connection point p22 between the resistors R13 and R14 is connected to the + terminal of the error amplifier circuit 8B.

In this example, a control circuit 19 is connected between the base of the transistor Q1 and the ground line GND, and based on at least the series voltage drop Vac detected by the input / output voltage detection circuit 18 and the voltage detection circuit 20. Thus, the internal resistance (internal resistance Rac) of the charge control transistor Q1 of the constant voltage / constant current circuit 21 is varied.
This is to protect the constant voltage constant current circuit 21.

The control circuit 19 includes resistors R3, R4, R1
1, R12 and a base current controlling transistor Q3,
Q4. One end of the resistor R3 is connected to the transistor Q1.
The other end of the resistor R3 is connected to the collector of the transistor Q3. An npn-type bipolar transistor is used as the transistor Q3. The output of the error amplifier 8A is connected to the base of the transistor Q3, and the emitter of the transistor Q3 is grounded through the resistor R4.

The input terminal a is connected to the emitter of the transistor Q2, and a base bias resistor R2 is connected between the base of Q2 and the emitter of Q1. Q2
Are connected to the base of Q1. A pnp type bipolar transistor is used as the transistor Q2.

The base of the transistor Q2 is connected to the collector of the transistor Q4 through the resistor R11, and the base of the transistor Q4 is connected to the output of the error amplifier 8B. The emitter of transistor Q4 is grounded through resistor R12. An npn-type bipolar transistor is used as the transistor Q4.

Next, an operation example of the charge control circuit 203 will be described. When, for example, an AC adapter having a large non-standard charging capability is connected to the input terminal ab shown in FIG. 7, the control circuit 19 reduces the internal resistance of the transistor Q1 as compared with the case where a standard AC adapter is connected. Control is performed to set r2.

That is, on the other hand, the output voltage VOUT divided by the resistors R5 and R6 is detected in the error amplifier circuit 8A, and the output voltage VOUT divided by the diode DZ1 and the resistor R7 is detected. The change is differentially amplified by the error amplifier circuit 8A. On the other hand, the input voltage VIN divided by the resistors R8 and R9 is detected by the error amplifier circuit 8B, the output voltage VOUT divided by the resistors R13 and R14 is detected, and these input voltage VIN and output voltage VOUT are error-corrected. The signal is differentially amplified by the amplifier circuit 8B.

The error voltage V generated by the above-described error amplification circuit 8A
Although ε1 is input to the base of the transistor Q3 of the control circuit 19, Vε1 has an output value several tens times higher than the standard value. Therefore, in the transistor Q3, the error amplifier circuit 8A
Is turned on based on the error voltage Vε1 that depends on the series voltage drop Vac detected by. The error amplifier circuit 8B
The error voltage Vε2 caused by the transistor Q
4, but the output value of Vε2 is several tens times higher than the standard value. Therefore, in the transistor Q4, the series voltage drop Va detected by the error amplifier circuit 8B is used.
It turns on based on the error voltage Vε2 that depends on c.

As a result, the base potential VBE of the transistor Q2 becomes lower, and the collector potential VBE of the transistor Q2 becomes lower.
CE rises, the base potential VBE of transistor Q1 falls, and transistor Q1 turns off. This is equivalent to a state in which the movable piece n shown in FIG. 2 has moved (closer to the output terminal c) as shown in FIG. 2 in which the internal resistance (the internal resistance Rac) of the transistor Q1 of the constant voltage / constant current circuit 21 is the largest.

If the series resistance Rac is r2 in this case, a fixed loss P0 ′ of I ′ ² · r2 occurs, but since the charging current I ′ is reduced to about several tenths compared with the standard time, The loss P0 and the fixed loss P0 ′ can be made substantially equal. Therefore, even when an AC adapter having a large non-standard charging capability is connected to the charging control circuit 203, heat generation in the constant voltage / constant current circuit 21 can be suppressed. The description of the operation when the AC adapter having the standard charging capability is connected is omitted.

(5) Fourth Embodiment FIG. 8 is a circuit diagram showing a configuration example of a charge control circuit 204 as a fourth embodiment according to the present invention. In this embodiment, a charge control circuit 204 is provided. This charge control circuit 204 includes an input fluctuation detection circuit 48 in addition to the output fluctuation detection circuit 20 according to the first embodiment. By controlling the internal resistance of the charge control transistor Q1 through the transistors Q2 to Q4, even when an AC adapter having a large non-standard charging capability is connected to the charge control circuit 204, the constant voltage / constant current circuit 21 is controlled.
To reduce the fixed loss consumed by
The configuration is such that heating of the constant voltage constant current circuit 21 can be prevented.

The charge control circuit 204 shown in FIG. 8 has an input fluctuation detection circuit 48, a control circuit 19, an output fluctuation detection circuit 20, and a constant voltage / constant current circuit 21. An input fluctuation detection circuit 48 is connected to an input terminal a of the constant voltage / constant current circuit 21. The input fluctuation detection circuit 48 includes an error amplification circuit 8B,
It has resistors R8 to R10 and a diode DZ2. The cathode of a constant voltage diode DZ2 is connected to the input terminal a through a resistor R10.
Is connected to the ground line GND to keep the input terminal ab constant. Where the diode DZ
The connection point between 2 and the resistor R10 is p22.

A resistance dividing circuit in which resistors R8 and R9 are connected in series is connected between the input terminals ab to detect an input voltage. A connection point p21 between the resistors R8 and R9 is connected to the minus terminal of the error amplifier circuit 8B,
The terminal has a connection point p2 between the diode DZ2 and the resistor R10.
2 are connected.

An output fluctuation detecting circuit 20 is connected to the output terminal c of the constant voltage / current circuit 21. The output fluctuation detection circuit 20 has an error amplification circuit 8A, resistors R5 to R7, and a diode DZ1. In this example, the constant voltage constant current circuit 21
The control circuit 19 is connected between the base of the transistor Q1 and the ground line GND, and the constant voltage constant current based on at least the series voltage drop Vac detected by the input fluctuation detection circuit 48 and the output fluctuation detection circuit 20. The internal resistance (internal resistance Rac) of the charge control transistor Q1 of the circuit 21 is varied. This is to protect the constant voltage constant current circuit 21. The components having the same names and the same reference numerals as those in the first embodiment have the same functions, and the description thereof will be omitted.

Next, an example of the operation of the charge control circuit 204 will be described. When, for example, an AC adapter having a large non-standard charging capability is connected to the input terminal ab shown in FIG. 8, the control circuit 19 reduces the internal resistance of the transistor Q1 as compared with the case where a standard AC adapter is connected. Control is performed to set r2.

That is, on the other hand, the output voltage VOUT divided by the resistors R5 and R6 of the output fluctuation detection circuit 20 is detected by the error amplifier circuit 8A, and the diode DZ
1. The output voltage VOUT divided by the resistor R7 is detected, and the change in the output voltage VOUT is differentially amplified by the error amplifier circuit 8A. On the other hand, the error amplification circuit 8
B has an input voltage VIN divided by resistors R8 and R9.
Is detected, the input voltage VIN divided by the resistor R10 and the diode DZ2 is detected, and these input voltages VIN are differentially amplified by the error amplifier circuit 8B.

The error voltage V generated by the above-described error amplification circuit 8A
Although ε1 is input to the base of the transistor Q3 of the control circuit 19, Vε1 has an output value several tens times higher than the standard value. Therefore, in the transistor Q3, the error amplifier circuit 8A
Is turned on based on the error voltage Vε1 that depends on the series voltage drop Vac detected by. The error amplifier circuit 8B
The error voltage Vε2 caused by the transistor Q
4, but the output value of Vε2 is several tens times higher than the standard value. Therefore, in the transistor Q4, the series voltage drop Va detected by the error amplifier circuit 8B is used.
It turns on based on the error voltage Vε2 that depends on c.

Thus, similarly to the third embodiment, the base potential VBE of the transistor Q2 decreases, the collector potential VCE of the transistor Q2 increases, the base potential VBE of the transistor Q1 decreases, and the transistor Q1 is turned off. . This is equivalent to a state in which the movable piece n shown in FIG. 2 has moved (closer to the output terminal c) as shown in FIG. 2 in which the internal resistance (the internal resistance Rac) of the transistor Q1 of the constant voltage / constant current circuit 21 is the largest.

If the series resistance Rac is r2 in this case, a fixed loss P0 ′ of I ′ ² · r2 occurs. However, since the charging current I ′ is reduced to about one-tenth of the standard value, The loss P0 and the fixed loss P0 ′ can be made substantially equal. Therefore, even when an AC adapter having a large non-standard charging capability is connected to the charging control circuit 203, heat generation in the constant voltage / constant current circuit 21 can be suppressed. The description of the operation when the AC adapter having the standard charging capability is connected is omitted.

(6) Mobile Phone FIG. 9 is a block diagram showing a configuration example of a mobile phone 101 as an embodiment of an electronic apparatus having a charge control function according to the present invention. In this embodiment, a mobile phone 101 having a charge control function, which is an example of an electronic device, is configured. The mobile phone 101 includes a charge control circuit 100, and a charger or an AC adapter having a large non-standard charging capability. Is connected to the charge control circuit 100, the charge control circuit 1
In this embodiment, the fixed loss consumed in 00 can be suppressed, and the mobile phone 101 can be prevented from being heated.

The portable telephone 101 shown in FIG.
5 is an example of an electronic device that operates using a driving power supply 5. The mobile phone 101 is connected to an AC adapter or the like having a predetermined charging capability, and charges the secondary battery 15 with a constant current and / or a constant voltage based on the AC adapter. The secondary battery 15 includes a Ni-Cd battery having an output voltage of about 4.2 V,
Lithium batteries are used. After charging, it is removed from the AC adapter and used. The mobile phone 101 includes a charge control circuit 100.

The charge control circuit 100 uses the charge control circuits 201 to 204 described in the first to fourth embodiments. For example, a charge control circuit 201 as the charge control circuit 100 is connected in series between the AC adapter 1 and the secondary battery 15 shown in FIG. The charging control circuit 100 includes a constant voltage / constant current circuit 21 for adjusting a charging current from the AC adapter to the secondary battery 15;
Output fluctuation detecting circuit 12 for detecting a series voltage drop based on the voltage between both ends of at least output fluctuation detecting circuit 1
And a control circuit 13 that varies the internal resistance of the constant voltage / constant current circuit 21 based on the series voltage drop Vac detected by the control circuit 2.

In this example, in the charging control circuit 100, when an AC adapter having a large non-standard charging capability is connected, the charging control circuit 100 has a higher charging capacity than when an AC adapter having a predetermined charging capability is connected. The internal resistance is increased.

A liquid crystal display (LCD) 23, a key array unit 27, a CPU 33, a ROM 34, a RAM 35, and an EEPROM are connected to the secondary battery 15 through a power switch SW.
The OM 36, the external interface (I / O) 37, the internal interface (I / O) 39, the wireless reception unit 41, the reception signal processing unit 42, the transmission signal processing unit 43, and the wireless transmission unit 44 are connected, and the power supply voltage is 4.2V. Is supplied.

Of course, when the power switch SW is turned on for these function processing circuits, the mobile phone 101 enters a standby state. The standby state means that the mobile phone 1
01 indicates a power saving state in which power is not supplied to the system LSI such as the LCD 23 and the CPU 33 except for the clock function.

The mobile phone 101 shown in FIG. 9 is provided with a CPU 33 for executing a wireless communication mode.
Is connected to an internal bus 38. This internal bus 38
Is connected to a wireless receiving unit 41, a received signal processing unit 42, a transmission signal processing unit 43, a wireless transmitting unit 44, and the like which constitute a wireless telephone function. Wireless receiver 41 and wireless transmitter 4
An antenna duplexer 45 is connected to 4 and is connected to the antenna 26.

In the radio receiving section 41, the power supply voltage of 4.2V is supplied from the secondary battery 15, and the radio wave received by the antenna 26 is separated from the transmission signal by the antenna duplexer 45 and the reception signal of the predetermined carrier frequency is received. Only is selected.
The received signal is amplified at a high frequency by a low noise amplifier or the like. The amplified received signal is mixed with the signal of the local oscillation frequency, and the intermediate frequency received signal is separated from the mixed signal. The received signal is subjected to quadrature demodulation processing after being amplified by the intermediate amplifier. The received signal after quadrature demodulation is analog
It is digitally converted to digital reception information.

After the control message and the voice compression information are demodulated from the received information, the error is corrected. The control message is output to the CPU 33. This audio compression information is output from the wireless reception unit 41 to the reception signal processing unit 42. In the reception signal processing unit 42, the power supply voltage of the secondary battery 15
In response to the supply of 2V, the audio compression information is decoded and expanded. The expanded audio information is digital-to-analog converted and then amplified and output from the speaker 24 for the receiver. The reception signal processing unit 42 includes a rear speaker 3
2 is connected, and a call is received with an onomatopoeic sound such as "beep, beep, beep ..." at the time of an incoming call.

A transmission signal processing unit 43 is connected to the microphone 28, and the power supply voltage of the secondary battery 15 is set to 4.2.
Upon receiving the supply of V, its own audio signal is amplified and then converted from analog to digital. The converted audio information is encoded and compressed. The encoded audio compression information is output from the transmission signal processing unit 43 to the wireless transmission unit 44.

In the radio transmission section 44, the power supply voltage of 4.2 V from the secondary battery 15 is supplied, the control message from the CPU 33 and the voice compression information are combined, and an error correction code is added. The transmission information after the sign is added is modulated.
The modulated transmission information is digital-to-analog converted. The converted transmission signal is amplified after being converted to an intermediate frequency transmission signal. The carrier frequency signal is modulated by the amplified transmission signal, power-amplified, and radiated from the antenna 26 toward the radio base station.

An EEPROM 36 is connected to the internal bus 38, and stores a control program for executing the wireless communication mode, the number of incoming calls, and the name of the other party. The EEPROM 36 also records telephone numbers such as speed dials. Further, a ROM 34 is connected to the internal bus 38, and each control program CP for controlling the entire mobile phone 101 is stored.

As for the control program CP, the display control of the liquid crystal display 23, the control procedure of the transmission processing using a communication modem such as the transmission signal processing 43 and the radio transmission section 44, and the communication of the radio reception section 41 and the reception signal processing 42 are performed. Describes a control procedure for reception processing using a modem. The control program CP is stored in the EEPROM 34 in addition to the EEPROM 34.
OM36 may be used. This is because the control program CP can be rewritten at the time of version upgrade.

Further, the liquid crystal display 23, the RAM 35, and the external I / O interface 37 are connected to the internal bus 38. The liquid crystal display 23 receives the power supply voltage of 4.2 V from the secondary battery 15 and receives the telephone number of the other party or own station, a message from the other party, character information to be transmitted to the other party, and various event information based on the control program CP. The contents are displayed. RAM
35 is used as a working memory, and the radio receiving unit 4
Character information such as a control message according to No. 1 and an absence message is temporarily recorded.

An I / O interface unit 39 is connected to the CPU 33, and the I / O interface unit 39
Is connected to an operation button 25 and a key array 27. A telephone number or the like is entered. An external I / O interface 37 is connected to the internal bus 38 to reach a USB terminal or the like for an external device (not shown), and information processing using an external personal computer, an external IC card, and a communication modem is expanded. It has been made possible. The DC power supply of these external devices may be used for the charger.

Next, an example of processing at the time of charging in the mobile phone 101 will be described. FIG. 10 is a flowchart illustrating an example of a process at the time of charging in the mobile phone 101. In this example, it is assumed that an AC adapter 1 having a standard charging capacity is connected.

With this as a charging condition, it is checked whether or not the AC adapter 1 is connected in step A1 of the flowchart of FIG. The check at this time is the user.
In the mobile phone 101, when the DC plug from the AC adapter 1 is inserted, the secondary battery 15
It is switched to 0. From this point on, the charging indicator lamp and the like are turned on. Normally, the secondary battery 15 is
Connected to each functional circuit.

Thereafter, at step A2, the charge control circuit 10
At 0, the voltage and the like at both ends of the constant voltage constant current circuit 21 and the like are detected. Then, in step A3, the internal resistance of the charge control transistor Q1 is adjusted. Here, this is equivalent to a state where the internal resistance (the internal resistance Rac) of the transistor Q1 is minimized and the movable piece n shown in FIG. 2 is moved (toward the input terminal a). The transistor Q1 in this case
Is the fixed resistance P0 of I ² · r1
Occurs. Thereafter, it is checked in step A4 whether charging is completed. The check at this time is the user. For this check, a method of confirming that the well-known charging indicator lamp or the like has been extinguished is adopted.

As described above, according to the portable telephone 101 as the embodiment according to the present invention, since the above-described charge control circuits 201 to 204 are applied to the charge control circuit 100, a nonstandard AC adapter is connected. Also in this case, the fixed loss consumed by the charge control circuit 100 can be kept low.

Therefore, it is possible to protect the mobile phone 101 that operates using the secondary battery 15 as a drive power source, not only when it is connected to an AC adapter having a predetermined charging capability, but also when a nonstandard AC adapter is connected. Can be.

In this embodiment, the electronic device is not limited to the case of the mobile phone 101, but is limited to the one driven by the secondary battery 15, for example, a game machine, a portable terminal device, a rechargeable shaving device. A similar effect can be obtained for a device, a rechargeable radio, and the like.

[0109]

As described above, according to the charge control circuit of the present invention, the charge control circuit for adjusting the charge current from the DC power supply to the secondary battery is provided. The internal resistance of the charging circuit is varied based on the series voltage drop.

With this configuration, when a DC power supply having a large non-standard charging capability is connected to the charging control circuit, for example, the internal resistance of the charging circuit is increased by the control circuit from the normal state. The charging current can be reduced as compared with the case where the battery is connected to a DC power supply having a predetermined charging capability. Therefore, even when a nonstandard DC power supply is connected, the fixed loss consumed in the charging circuit can be reduced, and heat generation in the charging circuit can be suppressed. The charging circuit can be protected.

According to the electronic device with a charge control function of the present invention, the above-described charge control circuit is applied. Therefore, even when a nonstandard DC power supply is connected, the fixed loss consumed by the charge circuit can be reduced. Can be suppressed.

Therefore, not only when the power supply is connected to a DC power supply having a predetermined charging capability but also when a non-standard DC power supply is connected, it is possible to protect the electronic equipment that operates using the secondary battery as the drive power supply. . INDUSTRIAL APPLICABILITY The present invention is very suitably applied to a battery-operated mobile phone, a mobile terminal device, a video camera, and the like.

[Brief description of the drawings]

FIG. 1 is a charge control circuit 1 according to an embodiment of the present invention.
It is a block diagram which shows the example of a structure of 00.

FIG. 2 is a diagram showing an example of an equivalent circuit of the charge control circuit 100.

FIG. 3 is a circuit diagram showing a configuration example of a charge control circuit 201 as a first embodiment according to the present invention.

FIG. 4 is a diagram illustrating an example of charging characteristics when an AC adapter having a predetermined charging capability is connected.

FIG. 5 is a diagram showing an example of charging characteristics when another AC adapter having a nonstandard charging capability is connected.

FIG. 6 is a circuit diagram showing a configuration example of a charge control circuit 202 as a second embodiment according to the present invention.

FIG. 7 is a circuit diagram showing a configuration example of a charge control circuit 203 according to a third embodiment of the present invention.

FIG. 8 is a circuit diagram showing a configuration example of a charge control circuit 204 according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram illustrating an example of an internal configuration of a mobile phone 101 as an embodiment of an electronic device with a charge control function according to the present invention.

FIG. 10 is a flowchart illustrating an example of a process at the time of charging in the mobile phone 101;

FIGS. 11A and 11B are image diagrams showing a charging example using an AC adapter 1 and a charger 2 according to a conventional example.

[Explanation of symbols]

11: charging circuit, 12, 20: output fluctuation detecting circuit, 13, 17, 19: control circuit, 16: input fluctuation detecting circuit, 18: input / output voltage detecting circuit, 21
..Constant voltage and constant current circuits, 100, 201 to 204,.
Charge control circuit, 101: mobile phone (electronic device)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H02J 7/10 H02J 7/10 HF term (Reference) 2G016 CB31 CC01 CC04 CC05 CC07 CC23 CD04 CD06 CD09 CD14 5G003 AA02 BA01 CA03 EA01 FA04 5H030 AA03 AS11 BB01 FF42 FF43

Claims (6)

[Claims] 1. A circuit that is connected to a DC power supply having a predetermined charging capability and controls charging so as to supply a constant current and / or a constant voltage to a secondary battery based on the DC power supply. A charging circuit that is connected in series with the secondary battery and adjusts a charging current from the DC power supply to the secondary battery; and a voltage that detects a series voltage drop based on a voltage across the charging circuit. A charging control circuit, comprising: a detection circuit; and a control circuit that varies an internal resistance of the charging circuit based on at least a series voltage drop detected by the voltage detection circuit. 2. The control circuit according to claim 1, wherein a DC power supply having a large non-standard charging capability is connected to the charging control circuit as compared with a case where a DC power supply having a predetermined charging capability is connected. The charge control circuit according to claim 1, wherein an internal resistance of the charge circuit is increased. 3. The charging control circuit according to claim 1, wherein the charging circuit includes a transistor that adjusts the charging current, and a constant current element that protects the transistor. 4. An electronic device which operates using a secondary battery as a drive power source, wherein the electronic device is connected to a DC power source having a predetermined charging capability, and supplies a constant current and / or a constant voltage to the secondary battery based on the DC power source. A charging control circuit that supplies a battery, wherein the charging control circuit is connected in series between the DC power supply and a secondary battery, and adjusts a charging current from the DC power supply to the secondary battery. A voltage detection circuit for detecting a series voltage drop based on a voltage between both ends of the charging circuit; and at least a variable internal resistance of the charging circuit based on the series voltage drop detected by the voltage detection circuit. An electronic device having a charge control function, comprising: 5. The control circuit according to claim 1, wherein a DC power supply having a large non-standard charging capability is connected to the charging control circuit, as compared with a case where a DC power supply having a predetermined charging capability is connected. The electronic device with a charge control function according to claim 4, wherein the internal resistance of the charging circuit is increased. 6. The electronic device with a charge control function according to claim 4, wherein the charging circuit includes a transistor that adjusts the charging current, and a constant current element that protects the transistor.